1. Glaciers What is a glacier? Formation of glacial ice
Glacial mass balance
Glacial flow
Types of glaciers
Glacial erosion and erosional landforms
Glacial deposition and depositional landforms
Ice ages—evidence and effects
Causes of ice ages (glaciation)

2. Glaciers Store 85% of fresh water on earth
Are sensitive to climate change--record past and present warming/cooling
>800 glaciers in WA
Melt produces 470 billion gallons of water each summer (decreasing)
Important effects on our landscape-most areas here affected by glacial erosion or deposition

3. What is a glacier? Accumulation of ice on land
By compaction and recrystallization of snow over a period of years
Moves under its own weight, after about 50m thick
Alpine glaciers: due to high altitude in mountains
Continental ice sheets at poles, or during ice ages; can form at low elevation

4. Snow Line: Elevation Above Which Snow
Snow Line: Elevation Above Which Snow Doesn’t Completely Melt in Summer

5. Valley Glacier Near Juneau, Alaska
See Fig

6. Through the Antarctic Ice Cap
Mountains Sticking Up
Through the Antarctic Ice Cap

7. Antarctic Ice Cap

8. Transformation of Snow to Glacial Ice Granular Ice (50% porosity
(Like metamorphism)
Snow 90% porosity
(Like Sand)
Granular Ice (50% porosity
(Like Sandstone)
Firn (20%)
Glacial
Ice (0% except
bubbles)
(Like quartzite)

9. Mosaic of Glacial Ice Crystals
Air Bubbles

10. Mass Balance or glacial ice budget: 1) the rate of glacial accumulation at the upper end of the glacier verses 2) the rate of glacial ablation (loss) at the lower end of the glacier.

11. Glacial Budget Equilibrium line or snow line (a visible feature)
Fig

12. Snow lines on two glaciers, Mt. Elbrus region, Caucasus, Russia
(end of summer season)

13. When glacial accumulation is greater than glacial ablation, the result is glacial growth and associated glacial erosion (by glacial plucking and abrasion).
Equilibrium line moves down-valley, terminus advances

14. When glacial accumulation is less than glacial ablation, the result is glacial retreat and associated glacial deposition.
Equilibrium line moves up-valley, terminus retreats
But ice still flows downhill!

15. Successive Stages of Ice Shelf Retreat

16. Animations of glacial advance and retreat

17. Plastic Flow: Glaciers Move by Plastic Flow and Basal Slip:
Individual ice crystals move microscopic distances over short periods of time (ductile)
Valley glaciers move mainly by plastic flow below about 40 m depth; top 40 m is brittle
Fig

18. Movement of a rigid ice slab along a base lubricated by water
Glaciers Move by Plastic Flow and Basal Slip:
Basal Slip:
Movement of a rigid ice slab along a base lubricated by water
Continental glaciers move mainly by basal slip
Fig

19. Mt. Formidable, N. Cascades
Crevasses: Cracks in the Glacier indicate brittle deformation near surface of ice
Mt. Formidable, N. Cascades
Crevasses tend to form where the valley curves or has a sudden change of slope (e.g. moves over steps in underlying bedrock

20. Ice plucks rock fragments, producing a rough surface
Glacial erosion:
Abrasion, plucking
Ice + ground up rock
polishes
smooth surface
Ice plucks rock fragments,
producing a rough surface

21. Abrasion by glaciers:
Glacial Polish, Striations, and Grooves Formed by Advancing Glacier and Exposed by Retreating Glacier in Glacier Bay National Park
See Fig

22. Erosional Landforms Associated with Valley Glaciation
U-shaped valleys
hanging valleys
fjords
horns
cirques
aretes

23. Glacial Erosion--Landforms
Before Glaciation
During Glaciation
After Glaciation

24. U-shaped valley, hanging valley, Yosemite

25. Fjord: a Drowned Glaciated Valley

26. Horn, aretes Switzerland

27. Horn, aretes North Cascades
Le Conte glacier, aretes, glacially polished surface
Sahale Mt.

28. Cirque: an amphitheater-shaped hollow formed at the head of a valley glacier
Fig

29. Types of Glacial Deposits
Glacial Drift: all deposits derived from a glacier
Glacial Till: material deposited directly from melting ice (unsorted, not bedded)
Glacial Erratic: large boulders within till
Glacial Outwash: glacial deposits that have been reworked by meltwater streams (sorted, bedded)

30. All Material Derived from Glaciers
Glacial Drift:
All Material Derived from Glaciers

31. Depositional Landforms Associated with Glaciation Include:
glacial moraines
end moraine
ground moraine
lateral and medial moraine
esker
drumlin
kettle lake
outwash plain

32. Lateral
Moraines
Medial
Moraines

33. Terminal (end) moraines and lateral moraines, Sierra Nevada
Evidence of past glacial advance, retreat

35. and landforms of continental glaciation
Glacial
Deposits
and landforms of continental glaciation

36. Present extent of permafrost in the northern hemisphere
Extent of glaciation in the northern hemisphere, based on the distribution of glacial drift
Fig

37. Effects of the last ice age
Last Glacial maximum advance 18,000 yrs ago
Sea level was lower (~120m)
Crust depressed by ice (isostasy)
Ecological changes--temp., food supply
Pluvial lakes (wetter climate)
Glacial lake Missoula, Great Salt lake
Temp. was lower, but average only 2-6°C
Landforms of continental glaciation

38. Extent and thickness of glacial ice and sea surface temperatures for a typical day in August, 18 ,000 years ago, during the last ice age.
See Fig

39. Evidence of Previous Ice Ages Late Paleozoic Glacial Deposits
~350 Million Years Old

40. Evidence of Previous Ice Ages Late Paleozoic Glacial Deposits
~350 Million Years Old
See focus on 1.1 for plate tectonic-ice age connection

41. Late Precambrian Glacial Deposits
~700 Million Years Old

42. Oxygen isotopes in marine microfossils record numerous glacial and interglacial periods
Focus on 14.3

43. The periodicity of glacial and interglacial cycles is best explained by cyclic variations in solar energy, governed by periodic variations in the Earth’s:
Eccentricity of Earth’s orbit around sun
Tilt of Earth’s rotation axis
Precession (rotational “wobble”)
These are called Milankovitch cycles

44. Orbital Eccentricity (~100,000 cycle)
Focus on 14.3, fig 2

45. Orbital Tilt (~41,000 cycle)
Focus on 14.3, fig 2

46. Orbital Precession (~23,000 cycle)
Focus on 14.3, fig 2